This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-10211 filed on Jan. 18, 2002.
1. Field of the Invention:
The present invention relates to a fuel injection device.
2. Description of Related Art:
In one known fuel injection device (also known as a fuel injection valve or injector), for example, for an internal combustion engine of a vehicle, a valve arrangement is driven by an electromagnetic drive unit to open and close fuel injection holes at variable and adjustable timing to precisely control the amount of fuel being injected from the fuel injection device.
In such a fuel injection device, a resin molded member (hereinafter, referred to as a resin outer cover member), such as a resin mold, serves as a securing means for securing corresponding components of the electromagnetic drive unit to the valve arrangement. That is, the resin molded member covers the components of the electromagnetic drive unit and joins them to the valve arrangement (as described in Japanese Unexamined Patent Publication No. 11-70347 corresponding to U.S. Pat. No. 5,931,391).
According to the Japanese Unexamined Patent Publication No. 11-70347, a metal inner tubular member, which serves as a stationary iron core, and two pieces of yokes are welded together with a drive coil sandwiched therebetween. Furthermore, the resin outer cover member is designed to fill a gap between the two pieces of yokes and the coil.
In the conventional structure, the metal inner tubular member, which is a component common to both the electromagnetic drive unit and the valve arrangement, is welded to the yokes, which are the components of the electromagnetic drive unit. Thus, in the case of the resin molded assembly, in which the components of the electromagnetic drive unit and the metal inner tubular member are integrated by the resin outer cover member through resin molding, it is required to prevent intrusion of foreign debris and also to prevent falling off of the components in manufacturing. This leads to additional costs associated with the manufacturing control.
Japanese Unexamined Patent Publication No. 11-513101 corresponding to U.S. Pat. No. 6,012,655 discloses a fuel injection device that addresses this issue. That is, components of the electromagnetic drive unit, which are arranged radially outward of the metal inner tubular member, are integrally resin-molded, and the metal inner tubular member and other components of the valve arrangement are assembled separately from the resin-molded components of the electromagnetic drive unit.
However, a magnetically connecting structure between the metal inner tubular member and the yokes in the fuel injection device disclosed in the Japanese Unexamined Patent Publication No. 11-513101 provides a simple contact between the metal inner tubular member and the yokes. In some instances, such a magnetic circuit may have a gap, which leads to inferior magnetic property and a slower response time in closing and opening of the valve arrangement.
Furthermore, the market continues to demand lower cost combustion engines that are also capable of achieving higher output power. In order to respond to such a need, the fuel injection device, which is a part of the internal combustion engine, must also offer a faster response time for opening and closing of the valve at a lower product cost.
The present invention addresses the issue described above by providing a fuel injection device that achieves a reduced product cost and stable magnetic property of a magnetic circuit.
To achieve the objective of the present invention, there is provided a fuel injection device that includes a metal inner tubular member, a drive coil arrangement, a metal outer frame member and a resin outer cover member. The metal inner tubular member receives a movable core and a valve member, which are joined to each other. The movable core and the valve member axially reciprocate in the metal inner tubular member. The metal inner tubular member constitutes a part of a magnetic circuit, which drives the movable core. The drive coil arrangement includes a coil and a bobbin. The coil generates electromagnetic force upon energization of the coil to activate the magnetic circuit. The coil is wound around the bobbin. The metal outer frame member is arranged radially outward of the metal inner tubular member in such a manner that the drive coil arrangement is radially positioned between the metal inner tubular member and the metal outer frame member. An end portion of the metal outer frame member is engaged with the metal inner tubular member to form another part of the magnetic circuit. The resin outer cover member at least partially covers an outer peripheral surface of the metal outer frame member all around the metal outer frame member. The resin outer cover member is joined to and covers the coil and the metal outer frame member. The metal inner tubular member has a step in an outer peripheral wall of the metal inner tubular member. An axial end surface of the end portion of the metal outer frame member axially abuts against the step of the metal inner tubular member.